This invention relates to an electromagnetic pump of the type having a built-in electromagnetic valve driven by a cyclically, intermittently supplied periodic current, such as a half-wave rectified current, a pulse current having a predetermined cycle, etc.
Heretofore, when a liquid disposed at a higher level than a pump is introduced into the pump for delivering the liquid under pressure or when a liquid disposed at a lower level than a pump is sucked into the pump for delivering the liquid under pressure, there has occurred a leak of the liquid due to the suction valve or discharge valve being opened by the pressure applied by the head of the liquid as the pump is rendered inoperative. In such occasion, the liquid not only has leaked but also has been ejected until the discharge pressure of the pump has dropped. Such phenomenon tends to cause a fire, production of an offensive smell or noxious gas due to incomplete combustion or explosion when the pump is an electromagnetic pump used with gun-type gas burner or other burner equipment wherein a fuel oil is supplied by the electromagnetic pump and burned after being ejected in jet streams under pressure. Incomplete combustion also causes deposition of soot on the nozzle of the burner and the nozzle becomes obturated, making it possible to eject the gaseous fuel in jet streams are required. This greatly reduces the reliability and the safety of use of the pump.
As a means for preventing such trouble, an electromagnetic value of an entity separate from the electromagnetic pump may be mounted on the suction side or discharge side of the pump. However, this requires more space than is necessary for mounting the electromagnetic valve and increases cost. Therefore, to avoid this disadvantage, proposals have been made to mount an electromagnetic valve in the electromagnetic pump structure.
Electromagnetic pumps having a built-in electromagnetic valve are disclosed, for example, in U.S. Pat. No. 3,874,822 (Japanese Patent Publication No. Sho 52-38243) and Japanese Utility Model Application Laid-Open Number Sho 54-159314 which corresponds to U.S. Pat. No. 4,252,505.
Electromagnetic pumps of the prior art having a built-in electromagnetic valve generally have a construction wherein a single electromagnetic coil produces a magnetic flux for actuating the pump and an electromagnetic flux for operating the electromagnetic valve or wherein a plurality of electromagnetic coils are arranged coaxially in adjacent relationship and the magnetic path for the magnetic fluxes produced by the two coils is in part shared by the two coils. In the electromagnetic pumps of the prior art having a built-in electromagnetic valve using a single coil or a plurality of coils having a common magnetic path, difficulties have been encountered in producing an optimum magnetic flux for each of the electromagnetic plunger and the electromagnetic valve operating movable member. As a result, in the electromagnetic pump using a single coil, microvibrations occur due to repeated attraction and repulsion of the electromagnetic valve operating movable member by the magnetic head caused by intermittent supply of a magnetic force of a periodic current energizing the coil and restitution elasticity of the return spring, causing noise or damage due to chattering. In the electromagnetic pump using a plurality of coils and having a common magnetic path, mutual interference of the magnetic fluxes produced by the two coils has the risk of preventing the electromagnetic valve and/or pump from operating in a normal fashin.